1. Field of the Invention
The present invention relates to a display device, specifically, to an active matrix display device.
2. Description of the Related Art
A rapid development has been made lately in a technique of manufacturing an electronic device, a thin film transistor (TFT), for example, in which a semiconductor thin film is formed on an inexpensive glass substrate. This is because there is an increasing demand for an active matrix liquid crystal panel.
The active matrix liquid crystal panel has a pixel portion in which several hundred thousands to several millions of TFTs are arranged in a matrix-like manner, and displays an image by controlling electric charges flowing in and out a pixel electrodes connected to each of the TFTs by means of switching function of the TFTs.
Conventionally, thin film transistors arranged in the pixel portion are fabricated using amorphous silicon that is formed on a glass substrate.
However, recent years have found a thin film transistor being formed from a polycrystalline silicon film while using quarts for a substrate. In this case, peripheral driver circuits are integrated with the pixel portion so that both the circuits and the pixel portion are formed on the quartz substrate.
There is also known a technique in which a thin film transistor is fabricated from a crystalline silicon film formed on a glass substrate by using laser annealing or other technologies.
What comes to draw attention recently, in addition to a large size active matrix liquid crystal panel used as a display device of a personal computer, is a small one that is to be used in a front projector, a rear projector, and an HMD (head mount display). Smaller is better for the small size active matrix liquid crystal panel used for these electronic devices, and now a panel sized about 0.7 inch, diagonally, has been set on mass production line.
Referring to FIG. 17, the structure of a conventional active matrix liquid crystal panel is shown schematically. In FIG. 17, reference numeral 11000 denotes a liquid crystal panel, 11100, a source driver, 11200, a gate driver, 11300, a pixel portion, and 11400, an FPC terminal. The FPC terminal is a terminal for inputting video data, a clock signal, a power supply, etc. to the liquid crystal panel. When the lateral length of the pixel portion is given as W and the longitudinal length thereof as H, W/H is generally 4/3 or 16/9.
Accompanying with the recent demand for downsizing, however, it is no longer uncommon cases that constructing the device in accordance with the circuit layout shown in FIG. 17 is impossible. For instance, in some liquid crystal panel, the size of its substrate has to be reduced in the longitudinal direction of the gate driver. In this case, the area the source driver occupies causes a problem. That is, the number of elements constituting the source driver is greater as compared with the gate driver, and accordingly the source driver occupies a larger area. The conventional circuit layout can not deal with the downsizing because of this large occupied area of the source driver.